The invention relates to a method for polar diagram forming in a connection between a subscriber and a base station with adaptive antenna arrangement in a radio communications system using multiple access methods.
Various concepts are known for improving the reception for connections between a subscriber and a base station in radio communications systems, in particular mobile radio systems.
By way of example, a first concept for this purpose uses a phased array antenna arrangement as the antenna arrangement at the base station for receiving subscriber signals in an uplink connection, with the antenna arrangement having a number of individual antennas and a number of polar diagrams. Each individual one of the polar diagrams is in this case currently aligned with a three-dimensional area, in order to supply this area. A subscriber signal which is sent by an individual subscriber is received as antenna signals via the individual antennas and depending on the number of the individual antennas, and these antenna signals are passed, with the aid of a common beam forming unit, as weighted sum signals to outputs of the beam forming unit. In this case, each output of the beam forming unit has one, and only one, associated polar diagram.
The weighted sum signals are passed to a user-specific polar diagram selection circuit, which is connected downstream of the beam forming unit, for further processing, the output from which once again contains not only the signal from a desired subscriber but also a subset of signals from further subscribers who are physically associated with the same polar diagram as the desired subscriber.
Thus, in this first concept, common polar diagram forming is carried out for all the subscribers, and for their subscriber signals, at the base station. Depending on their respective location, the individual subscriber signals are effectively amplified or attenuated on reception by the polar diagrams and by their polar diagram characteristic, with each individual polar diagram once again being associated with one, and only one, of the outputs of the beam forming unit.
The implementation of the first concept, which can be carried out in a very robust manner, makes it possible to improve both the supply and the system capacity of the radio communications system. Furthermore, it is possible to suppress disturbing interference signals from subscribers who are located, in comparison to a first subscriber, in a physical area which is associated with an adjacent polar diagram. It is impossible to suppress disturbing interference signals from subscribers who are supplied jointly using the same polar diagram.
The three-dimensional resolution is reduced by selecting a limited number of preformed polar diagrams.
In a second concept, an antenna arrangement with individual antennas is used for receiving subscriber signals at the base station. However, there is no longer rigid association between fixed polar diagrams or physical areas and the subscribers, and the antenna signals which are received by the individual antennas are instead of this processed directly and on a user-specific basis, that is to say the individual antenna signals are adaptively combined with one another. In radio communications systems using CDMA multiple access methods, this is done, by way of example, using an “eigen beam former”.
This second concept is characterized by the radio communications system having a full adaptation capability to the respective transmission and interference situation. Good capabilities to suppress disturbing interference signals are obtained by technically proven algorithms and user-specific, adaptive calculation of any desired polar diagrams (beams). This makes it possible to optimize a received signal in terms of noise and interference, and this is done using a signal-to-noise and interference ratio value (SINR).
However, this involves a high level of complexity and increased computation complexity owing to the user-specific processing of the subscriber signals, for example by the eigen beam former, and this is particularly true when processing spread spectrum received signals.